Electric cables for solar plants generating electrical  and thermal energy, and plants comprising the electrical cables

ABSTRACT

A composite flat cable, having in cross-section a major side, may include an outer sheath; two main electrical conductors; and two ducts for fluid circulation configured to circulate fluid. A composite flat cable may include two ducts configured to circulate fluid; a first main electrical conductor on a first side of the two ducts; a second main electrical conductor on a second side of the two ducts; and a sheath around the two ducts, the first main electrical conductor, and second main electrical conductor. A solar cogeneration plant may include at least one cell configured to produce electric current, connected to a plant for distribution of electrical energy and of heated fluid by a composite flat cable.

The present invention relates to an electric cable. In particular, thepresent invention relates to an electric cable for a solar plant forgenerating electrical energy and thermal energy. The present inventionalso relates to a solar plant comprising said cable.

Solar plants for generating electrical energy from solar radiation areknown. By way of example, photovoltaic plants generating electricalenergy by converting solar radiation by means of photovoltaic modulesare known.

Solar plants for generating heat are also known. Generally, these solarplants heat up a fluid, for example water.

Finally, hybrid solar plants affording electrical energy and thermalenergy generation are known. Such plants are also known as “solarcogeneration” plants. Hereinbelow, as “solar cogeneration plant” it ismeant a plant able to convert solar radiation into electrical energy andinto thermal energy.

Typically, a solar cogeneration plant comprises at least one cellproducing electric current, for example a photovoltaic cell, andoptionally a solar radiation concentrator. Typically, a cogenerationplant comprises at least one surface exposed to the solar radiation and,optionally, capable to orient itself to follow the path of the sun. Theconcentrator provides for obtaining a greater solar radiation (photons)density on the cell.

Typically, a solar cogeneration plant also comprises an electric circuitfor transporting the generated electrical energy and a hydraulic circuitfor transporting the heated fluid. The electric circuit, in turn,comprises two electric conductors and the hydraulic circuit, in turn,comprises two ducts, one for the fluid to be heated and one for theheated fluid.

The Applicant has found that the management in situ of electricconductors, of the relative electric connectors, of ducts for fluidtransportation and of the relative connections is complex and ratherinconvenient, since the installer has to take care not to cast thecables and tubes shades onto the concentrator or onto the surfaceexposed to the sun, and also has to check the correct relativepositioning of conductors and tubes, which involves a longerinstallation time and therefore higher costs. Moreover, an installercould make errors and carry out connections which are incorrect or,anyway, which do not guarantee the safety and the efficiency of theplant.

The Applicant set themselves the target of improving the management ofthe electric conductors and of the ducts for fluid transportation in asolar cogeneration system.

The Applicant perceived that the above mentioned target can be achievedby organizing electric conductors and ducts for fluid transportation ina single cable of a flat configuration (where the internal elements arearranged with longitudinal axes that are substantially parallel and liein the same plane).

With respect to a cable having a circular cross section, a flat cablehas disadvantages in terms of flexibility as it can be easily folded intwo directions only. Therefore, the selection of a flat cable forfacilitating the installation and the management of a solar cogenerationplant may not be advantageous prima facie.

However, the Applicant found that the organization of electricconductors and ducts for fluid transportation in a single flat cable hassurprising advantages, as will be explained hereinbelow.

WO 2012/079631 describes a high voltage electric cable comprising atleast one cable core, at least one cooling pipe for cooling the cablecore adapted for carrying a cooling fluid, and a cable coveringenclosing the at least one cable core and the at least one cooling pipe.The electric cable further comprises at least one heat conductingelement surrounding the at least one cable core, and being arranged inthermal contact with the at least one cable core and the at least onecooling pipe.

GB 1368497 describes an electric power cable assembly which comprises anelectric power cable having a duct along the length thereof forcirculating an evaporable refrigerant to cool the cable.

GB 875930 describes a heavy-current electric cable comprising aninsulated metal-sheathed core enclosed in an outer impermeableprotective covering of plastic material in which a plurality of ducts orchannels are provided for the circulation of a cooling fluidtherethrough.

The solutions above relate to electric cables containing ducts forcirculating a fluid suitable for keeping the temperature of the cablewithin defined limits.

The fluid of the circulation system of the present invention heats upand substantially retains the heat acquired along the entire extensionof the cable, making it available to a user of the cogeneration system.

In a first aspect, the present invention relates to a composite flatcable having, in cross section, a major side, and comprising two mainelectric conductors and at least two ducts for fluid circulation.

Advantageously, the main electric conductors are arranged in proximityof one end of the major side of the composite cable.

For the purposes of the present description and claims, the term“composite cable” denotes a cable comprising electric conductors, alsoconfigured to transport currents of differing value, together with otherelements having a different function, for example tubes for fluidtransportation.

For the purposes of the present description and claims, the term “flatcable” denotes a cable in which the internal elements are arranged withlongitudinal axes substantially parallel and lying in the same plane.

Typically, the shape of a flat cable in cross section, considered on aplane transverse to the longitudinal axis of the cable, is substantiallyrectangular. It preferably has rounded edges. The major side of thiscross section is referred to as the width and the minor side is referredto as the height. Preferably, the width of the cross section of thecable is at least twice the height of the cross section of the cable.More preferably, the width is at least three times the height.

For the purposes of the present description and claims, the term“electric conductor” denotes a conductive metal, generally in form ofjoint wires, surrounded by concentric layers having various functions,including electrical insulation.

Preferably, the two ducts for fluid circulation are each arrangedalongside one of the main electric conductors, in an inner position withrespect to the corresponding end of the major side of the compositecable.

Advantageously, the cable of the present invention comprises at leastone further conductor, referred to as a secondary conductor. Preferably,these secondary conductors are arranged in a position innermost thanthat of the two ducts for fluid circulation with respect to the ends ofthe major side of the cable.

The secondary conductors can have electrical connection functions, forexample to service sensors of the plant. The electrical capacity of thesecondary conductors is, however, smaller than that of the mainconductors. The secondary conductors can comprise optical conductors.

Preferably, the cable of the invention comprises an outer sheathsurrounding at least the two main electric conductors and the two ductsfor fluid circulation, and based on cross-linked ethylene/vinyl acetatecopolymer, optionally added with an anti-UV additive.

Preferably, the outer sheath is added with a flame retardant additive.Examples of flame retardant additives are aluminium hydroxide andsynthetic or natural magnesium hydroxide.

Advantageously, each main electric conductor comprises a conductive coreformed by a plurality of copper conductors, each optionally covered by alayer of tin. Preferably, the conductive core is a class 5 conductoraccording to EN 60228 2004-11 standard.

Preferably, the conductive core of each main electric conductor issurrounded by one or more tapes of nonwoven fabric.

Advantageously, each duct for fluid circulation comprises a corrugatedtube, preferably of stainless steel.

Each duct for fluid circulation preferably comprises a silicone layer ina radially outer position with respect to the corrugated tube.Advantageously, a braid of wires is arranged between the corrugated tubeand the silicone layer.

In a second aspect, the present invention relates to a solarcogeneration plant comprising at least one cell adapted to produceelectric current, connected to a plant for the distribution ofelectrical energy and hot fluid by a composite flat cable having, incross section, a major side and comprising two main electric conductorsand at least two ducts for fluid circulation, the main electricconductors being arranged each at an end of the major side of the cable.

Cells adapted to produce electric current are preferably chosen fromamong photovoltaic, thermoelectric or thermionic cells.

Advantageously, the cogeneration plant of the present inventioncomprises a solar radiation (photons) concentrator.

Advantageously, the cogeneration plant of the invention comprises atleast one surface exposed to the solar radiation and, preferably, ableto orient itself to follow the path of the sun.

The present invention will become clearer in the light of the followingdetailed description, which is provided purely by way of non-limitingexample and is to be read with reference to the enclosed drawings, inwhich:

FIG. 1 is a schematic cross section of a cable according to a firstembodiment of the present invention;

FIG. 2 is a schematic cross section of a cable according to a secondembodiment of the present invention;

FIG. 3 is a schematic cross section of a cable according to a thirdembodiment of the present invention; and

FIG. 4 schematically shows a solar cogeneration plant comprising astretch of cable according to the present invention.

FIG. 1 is a schematic cross section of a cable 10 according to a firstembodiment of the present invention.

The cable 10 comprises an outer sheath 2 made of polymer materialresistant to UV rays. In one embodiment, the outer sheath is made of apolymer resistant up to about 120° C. for at least 20 years according toArrhenius' aging model, and flexible, for example a cross-linkedethylene/vinyl acetate copolymer mixed with anti-UV additive. Thismaterial is particularly advantageous in that it affords goodflexibility, resistance and interstitial filling.

Advantageously, the polymer material of the outer sheath 2 is flameretardant, i.e. it is able to resist fire and to delay the propagationthereof in accordance to IEC 332-1 (1993) and IEC 332-3 (1992)standards.

In one embodiment, the cable 10 has a width L of from about 30 mm toabout 40 mm and a height H of about 15-20 mm, for example 18 mm.

Preferably, the cable 10 of the present invention is a cable which, asseen in cross section with respect to the longitudinal axis, is roughlyrectangular with short sides formed by curved lines, for example bysemicircles, as shown in FIG. 1.

The cable 10 has a longitudinal axis 11. FIG. 1 also shows the paths oftwo planes X-X and Y-Y, which are perpendicular one another and passthrough the longitudinal axis 11. The cable 1 shown in FIG. 1 ispreferably symmetrical with respect to the plane X-X and to the planeY-Y.

The cable 10 comprises two main conductors 3 a and 3 b and two ducts 5 hand 5 c for fluid transportation. The two conductors 3 a and 3 b arealike. For descriptive convenience, these will be denoted simply by thenumeral 3. Similarly, the ducts 5 h and 5 c too are alike, and, fordescriptive convenience, will be denoted simply by the numeral 5. Theletters “a”, “b”, “c” and “h” will be used, for example, when describingthe simulations carried out on the cable of the present invention.

As schematically shown in FIG. 1, the two main conductors 3 arepreferably arranged at the two lateral ends La and Lb of the cable 10,that is with the greatest axial spacing with respect to the plane Y-Y.Each main conductor 3 preferably comprises, from the centre outwards, aconductive core 31, a first tape 32, for example made of polyester,which extends longitudinally around the core 31, an inner insulatinglayer 33 and a second tape 34.

The conductive core 31 is advantageously formed by a plurality of copperconductors, each optionally covered by a layer of tin. Advantageously,the conductive core is a class 5 conductor according to EN 60228 2004-11standard. Conductive cores having such a structure have markedflexibility characteristics facilitating the installation of the cableand the operation thereof, especially in a plant equipped with a surfaceexposed to the solar radiation and able to orient itself to follow thepath of the sun, when the cable is subjected to twisting.

The inner insulating layer 33 can be made of silicone material, forexample Elastosil R 501/75 MH L8-0 C6 Black 9005 RM041271, or of apolymer, such as an ethylene/propylene copolymer. Advantageously, thelayer 33 has flame retardant characteristics as mentioned above.

The second tape 34 can advantageously be in the form of a nonwovenpolyester tape.

The tapes 32 and/or 33 ease the process of stripping the conductive core31, for example when it is necessary to connect the conductive core 31to other electric elements or components (not shown).

In one embodiment, the outer diameter of the main conductor 3 is about13 mm.

In the embodiment shown in FIG. 1, the ducts 5 for fluid transportationhave a roughly circular cross section and are advantageously arranged inan axially inner position with respect to the two main conductors 3.

Preferably, the two ducts 5 for fluid transportation are arrangedsymmetrically with respect to the plane Y-Y, i.e. the centres thereof,positioned substantially on the plane X-X, are substantially at the samedistance with respect to the plane Y-Y.

In one embodiment, each duct 5 comprises a corrugated tube 51,preferably of stainless steel. The tube 51 can have an inner diameter ofabout 6 mm and an outer diameter of about 9.5 mm.

Preferably, a layer 52 of nonwoven tape, for example of polyester, iswound around the corrugated tube 51, with a minimum overlap equal to,for example, about 25%.

Preferably, the duct 5 also comprises, in a radially outer position withrespect to the layer 52, a braid of polyester wires (not shown) and, inan outer position with respect thereto, a silicone layer 53, for exampleElastosil R 501/75 MH L8-0 C6 5015 RM042438. The braid advantageouslyallows extruding the next layer 53 around the corrugated elements of thetube 51. Advantageously, the braid angle is less than 30° with respectto the longitudinal axis of the tube.

Preferably, the duct 5 also comprises, in a radially outer position withrespect to the silicone layer 53, a further layer 54 of nonwovenpolyester tape, with a minimum overlap equal to, for example, about 25%.

The duct 5 can also comprise, in a radially outer position with respectto the layer 54, a further layer of polyester tape (not shown).

Advantageously, the outer diameter of the duct 5 is substantiallyidentical to the outer diameter of the main conductors 3, for exampleabout 13 mm.

The two ducts 5 form a circuit for fluid transportation: one of the twoducts (that denoted by 5 c) carries fluid to be heated whereas the otherof the two ducts (that denoted by 5 h) carries heated fluid.

FIG. 2 is a schematic cross section of a cable 20 according to a secondembodiment of the present invention. The cable 20 comprises elementssimilar to those of the cable 10, and these have been denoted by thesame reference numerals as used in FIG. 1. This cable too issubstantially preferably symmetrical with respect to the plane X-X andto the plane Y-Y.

In addition to the elements already present also in the cable 10, thecable 20 comprises a secondary electric conductor intended to connectdetection/diagnosis sensors, the sensory conductor 7. The latter ispreferably arranged in an axially inner position with respect to the twoconductors 3 and to the two ducts 5. This arrangement is advantageousbecause it affords a cable symmetrical with respect to the plane Y-Y.Moreover, it allows keeping the main conductors 3 at the ends of thecable and the ducts 5 alongside the conductors 3 (for reasons which willbe explained more clearly hereinbelow). In the embodiment shown in FIG.2, the sensory conductor 7 is arranged between the two tubes 5.

The sensory conductor 7 comprises a plurality of suitably twisted copperpair wires 71. By way of example, it comprises four copper pair wires.The pair wires can have a cross-sectional area of 0.75 mm², for example.

In a radially outer position with respect to the pair wires 71, aninsulation 72 is provided, for example made of ethylene vinyl acetate(EVA), with a thickness of about 0.6 mm for example.

Preferably, a thickness 73 made of a silicone material is arranged in aradially outer position with respect to the insulation 72.

Preferably, a layer 74 made of nonwoven polyester tape is provided in aradially outer position with respect to the thickness 73.

A braid of polyester wires (not shown) can be provided in a radiallyouter position with respect to the layer 74. Said braid advantageouslyhelps a stable extrusion process.

A further layer made of a nonwoven polyester tape (not shown) can beprovided in a radially outer position with respect to said braid.

In a preferred embodiment, the outer diameter of the sensory conductor 7is substantially identical to the outer diameter of the main conductor3, for example about 13 mm.

In one embodiment, the cable 20 has a width L of from about 40 mm toabout 50 mm and a height H of about 15-20 mm, for example 18 mm.

FIG. 3 is a schematic cross section of a cable 30 according to a thirdembodiment of the present invention. The cable 30 comprises elementssimilar to those of the cable 10 and of the cable 20, and these havebeen denoted by the same reference numerals as used in FIGS. 1 and 2.

In addition to the elements present also in the cable 10 and 20, thecable 30 comprises a secondary electric conductor 9. The secondaryconductor 9 has a current rating less than that of the main conductors 3and, as a result, develops less heat. In view of this, according to thepresent invention, it is preferably arranged in an axially innerposition both with respect to the main conductors 3 and to the tubes 5for fluid transportation.

The secondary conductor 9 comprises, for example, two conductive cores91 having a diameter, for example, of about 9.5 mm. The conductive cores91 are made up of stranded copper wires, each optionally covered by alayer of tin, and advantageously of class 5 according to EN 602282004-11 standard.

Preferably, the conductive cores 91 are stranded with auxiliarystranding elements 93, obtained for example by the extrusion of apolymer on a yarn support.

An insulating layer 92, for example made of silicone material, isprovided in a radially outer position with respect to the conductivecores 91 and, if appropriate, to the filler elements 93. The insulatinglayer 92 can have a thickness of about 0.9 mm.

Preferably, a layer of tape 94, for example made of nonwoven polyester,is provided in a radially outer position with respect to the insulatinglayer 92.

In a radially outer position with respect to the layer of tape 94, athickening section 95 is provided, for example made of siliconematerial, which preferably, in turn, is covered with a braid 96, forexample of polyester threads. The braid 96 advantageously improves theextrusion of the outer sheath 2.

Preferably, a tape (not shown), for example made of nonwoven polyester,is provided in a radially outer position with respect to the braid 96.

Preferably, the outer diameter of the secondary conductor 9 issubstantially identical to the outer diameter of the main conductor 3,for example about 13 mm.

In the third embodiment, the cable 10 has a width L of from about 50 mmto about 70 mm, for example about 60 mm, and a height H of about 15-20mm, for example 18 mm.

In all of the three embodiments, it is preferable that the conductorsand the ducts of the hydraulic circuit have substantially the samediameter. Preferably, the conductors and the ducts of the hydrauliccircuit are arranged such that the longitudinal axis thereof lies on thesame plane (X-X), which is the preferential bending plane of the cable.

FIG. 4 shows an exemplary diagram of a concentrating solar cogenerationplant according to one embodiment of the present invention. The plant100 comprises a surface 101 exposed to solar radiation (having a concaveshape), and a cell 102 adapted to produce electric current and alsoincluding a heat exchanger (not shown in detail). The cell 102 convertsthe concentrated solar flux into electrical energy and into thermalenergy. By way of example and with preference, the thermal energy isthen transferred to a fluid pumped through a closed circuit and thenconveyed to a user or a plant 103. Advantageously, the surface exposedto solar radiation is mounted on a support 104 by means of arms 106,capable of following the path of the sun by moving along two axes.

The cell 102 is connected to the user 103 by means of a cable length 30according to the present invention. The cable can be in accordanceeither with the first embodiment, the second embodiment or the thirdembodiment.

As can be seen in FIG. 4, the cell 102 is supported by an arm 105 and isconnected to the cable 30. The presence of the arm and of the cablecreates areas of shade on the surface exposed to solar radiation. Theseareas of shade can reduce the efficiency of the plant. Advantageously,the cable according to the present invention has a reduced cross section(height H) and can be arranged in such a way as to create a reduced areaof shade. Indeed, the cable can be arranged edgeways, that is in such amanner that the shade projected onto the surface 101 is given by thelength of the cable multiplied by the width H. This width H is smallerthan the diameter of a cable having a circular cross section (not shown)incorporating two main conductors having the diameter of the conductors3 and two ducts having the diameter of the ducts 5.

Therefore, advantageously, the flat cable according to the presentinvention increases the efficiency of a solar cogeneration plant in thatit creates less extensive areas of shade.

In other embodiments (not shown), the solar cogeneration plant couldcomprise a first stage of generating electrical energy by thermioniceffect (where the solar radiation heats up a ceramic component whichemits electrons through thermionic effect). The current thus generatedis of the order of 100 or 200 A, at a low voltage. The plant couldfurther comprise a second stage of generating electrical energy bythermoelectric effect (through a known thermoelectric generator). Thecurrent thus generated would have a value which is less than thatgenerated by thermionic effect, but at a higher voltage. The plant couldfurther comprise a third stage (hydraulic or thermal stage) for heatingup a fluid (for example water), making it circulate at a temperature ofabout 90° C.

Advantageously, the plant of the present invention can provide forarranging the main conductors (those carrying a high current at a lowvoltage) at the ends of the cable of the invention. This affords animproved dispersion of the heat generated by the high current. Indeed,the heat can be dispersed onto a wider surface.

The innermost part of the cable of the invention can instead bededicated to the water tubes. These remain better protected andinsulated and disperse less heat than they would disperse if they werepositioned in the outermost positions, to make it available then to thefinal user.

In the second and in the third embodiment, the conductors for the sensordevices are housed between the fluid ducts. These produce little heatsince the current required to feed the sensors is typically very small(of the order of 100 mA), and therefore they do not require extensivedissipation areas. Furthermore, advantageously, they are mechanicallyprotected just because of their central location.

Analogously, the secondary conductors of the third embodiment are alsoarranged in the central part of the cable. Actually, these carry arelatively low current generating a relevant reduced heat.

The cable configuration of the invention also maximizes the solarradiation collected. Indeed, when the cable lies on the ground T, itstays flat, with one face in contact with the ground and one faceexposed to the sun. The face exposed to the sun tends to heat up andtherefore to maintain (or even increase) the temperature of the fluid inthe ducts 5. The opposite face, instead, is insulated by the ground T.The heat losses will thereby be greatly reduced through that face.

Finally, the provision of a cable structure comprising both conductorsand ducts for fluid transportation in an optimized configuration makesthe installation operations quicker and more practical, and avoidsinstallation errors.

Contrary to the solution described in WO 2012/079631, according to thepresent invention, the conductors are not in thermal contact with thetubes which carry heated fluid. Indeed, the conductors 3 and 9 arecompletely surrounded by the outer sheath 2. Similarly, the tubes 5 tooare completely surrounded by the outer sheath 2.

The Applicant carried out tests using a cable according to the thirdembodiment.

1^(st) Test

The conditions of the first test are shown in Table 1.1.

TABLE 1.1 Position of the cable: Cable lying on the ground, horizontalposition Solar flux: 1000 W/m² flux directed onto the top face Electriccurrent: Maximum value: 200 A in the main conductors 3a and 3b; 20 A inthe secondary conductor 9 Ambient temperature: 50° C. Water temperatureHot tube 5h: 95° C. Cold tube 5c: 85° C.

The results of the first test are shown in Table 1.2.

TABLE 1.2 Max. temperature of the conductors 3a, 3b 122.6° C. Max.temperature of the secondary conductor 7 117.8° C. Max. temperature ofthe sheath 121.4° C. Heat flux in the hot tube 5h 4.7 W/m Heat flux inthe cold tube 5c 6.8 W/m

It is clear that the cable 30 according to the third embodiment of thepresent invention, when resting on the ground and in extreme conditions(maximum current in the main conductors and very high externaltemperature), had a positive heat flux, i.e. it made the fluid in thetubes not losing heat, but rather increasing it. Advantageously, even inthese extreme conditions, no component of the cable reached hightemperatures (with respect to the materials used). The maximumtemperature reached by the main conductors was indeed about 120° C. Thismakes it possible to ensure a service life of the cable of 25 yearsusing the materials mentioned above. By changing materials, it could bepossible to ensure a different service life at this maximum temperature.

2^(nd) Test

The conditions of the second test are shown in Table 2.1.

TABLE 2.1 Position of the cable: Cable attached to the support arm;vertical position edgeways Solar flux: 400 W/m² flux directed onto theshort side closest to the conductor 3b; 70 W/m² flux diffused onto thetop and bottom faces Electric current: Maximum value: 100 A in the mainconductors 3a and 3b; 10 A in the secondary conductor 9 Ambienttemperature: 20° C. Water temperature: Hot tube 5h: 95° C. Cold tube 5c:85° C.

The results of the second test are shown in Table 2.2.

TABLE 2.2 Max. temperature of the conductors 3a, 3b 73.5° C. Max.temperature of the secondary conductor 7 69.0° C. Max. temperature ofthe sheath 85.0° C. Heat flux in the hot tube 5h −17.5 W/m Heat flux inthe cold tube 5c −11.9 W/m

It is clear that the cable 30 according to the third embodiment of thepresent invention, when arranged vertically in real conditions, had ajust slightly negative heat flux, i.e. it made the fluid in the tubes tolose little heat.

1. A composite flat cable having in cross-section a major side, thecable comprising: an outer sheath; two main electrical conductors; andtwo ducts configured to circulate fluid.
 2. The cable of claim 1,wherein each of the main electrical conductors is arranged in proximityof a corresponding end of the major side of the cable.
 3. The cable ofclaim 1, wherein the two ducts configured to circulate fluid are eacharranged alongside one of the main electrical conductors, in an innerposition with respect to a corresponding end of the major side of thecable.
 4. The cable of claim 1, further comprising: at least onesecondary electrical conductor.
 5. The cable of claim 4, wherein the atleast one secondary electrical conductor is arranged in a positioninnermost than that of the two ducts configured to circulate fluid withrespect to the ends of the major side of the cable.
 6. The cable ofclaim 1, wherein the outer sheath is based on cross-linkedethylene/vinyl acetate copolymer.
 7. The cable of claim 1, wherein eachof the main electrical conductors comprises a conductive core includinga plurality of copper conductors.
 8. The cable of claim 7, wherein theconductive core is a class 5 conductor according to the EN 60228 2004-11standard.
 9. The cable of claim 1, wherein each of the ducts comprises:a corrugated tube.
 10. The cable of claim 9, wherein each of the ductscomprises: a silicone layer in a radially outer position with respect tothe corrugated tube.
 11. A solar cogeneration plant, comprising: atleast one cell configured to produce electric current, connected to aplant for distribution of electrical energy and of heated fluid by acomposite flat cable, having in cross-section a major side, the cablecomprising: an outer sheath; two main electrical conductors; and twoducts configured to circulate fluid.
 12. The cable of claim 1, whereinthe outer sheath is based on cross-linked ethylene/vinyl acetatecopolymer with an anti-ultraviolet (UV) additive.
 13. The cable of claim1, wherein the outer sheath is based on cross-linked ethylene/vinylacetate copolymer with a flame-retardant additive.
 14. The cable ofclaim 9, wherein the corrugated tube comprises stainless steel.
 15. Thecable of claim 9, wherein each of the ducts comprises: a silicone layerin a radially outer position with respect to the corrugated tube; and abraid of wires between the corrugated tube and the silicone layer.
 16. Acomposite flat cable, comprising: two ducts configured to circulatefluid; a first main electrical conductor on a first side of the twoducts; a second main electrical conductor on a second side of the twoducts; and a sheath around the two ducts, the first main electricalconductor, and second main electrical conductor.
 17. The cable of claim16, wherein in cross-section, the cable is symmetric with respect to acenterline of the cable that includes the two ducts, the first mainelectrical conductor, and second main electrical conductor.
 18. Thecable of claim 16, wherein in cross-section, the cable is symmetric withrespect to a centerline of the cable that is perpendicular to a linethat includes the two ducts, the first main electrical conductor, andsecond main electrical conductor.
 19. The cable of claim 16, furthercomprising: at least one secondary electrical conductor between the twoducts.
 20. The cable of claim 19, wherein a current rating of the atleast one secondary electrical conductor is less than a current ratingof the first main electrical conductor, and wherein the current ratingof the at least one secondary electrical conductor is less than acurrent rating of the second main electrical conductor.